This invention relates generally to video computer systems, and more particularly, to a video computer system which employs at least two alternative video graphics controllers, thereby enabling the video computer system to compatibly execute graphics programs selected from two generally incompatible libraries of programs.
The video computer technology, especially in the video game and home computer industries, has developed rapidly in recent years. As each new video computer system (VSC) is marketed, video software development firms introduce new and improved video software programs which are compatible with the improved VCS. In many cases, the newly released VCS may not be compatible with its predecessor models. As a result, software designed to be executed on one VCS may not be compatibly executed on another. Since the cost to the consumer of software may, over a period of time, far exceed the cost of the computer system, it is desirable to offer consumers an improved VCS which is capable of executing not only the newly developed programs, but also programs selected from a library of previously published programs designed for an earlier model VCS.
For example, an early VCS employed a video graphics controller disclosed in U.S. Pat. No. 4,112,422 to Mayer, et al. (referred to below as the "Mayer '422 Patent"), entitled "Method and Apparatus For Generating Moving Objects On A Video Display Screen," herein incorporated by reference. The heart of the Mayer '422 Patent is a video graphics controller which is known in the industry as the Television Interface Adaptor, or "TIA" for short. The TIA was an immediate market success and was the subject of two trade articles: Design Case History: The Atari Video Computer System (Perry and Wallich, IEEE Spectrum, March 1983), and Video Games Enter Technology Time Warp (Brody, High Technology, June 1983). Many software development firms introduced video programs to be compatibly executed on the Artari TIA, with the result that a library presently exists comprising literally hundreds of programs compatibly designed solely for the Atari TIA.
As technological advances made apparent the limits of the Atari TIA, advanced programming techniques and/or a new VCS employing an improved graphics controller were needed in order to satisfy consumer needs for more complex graphic displays. One such advanced programming technique for the Atari TIA is disclosed in a co-pending application, Ser. No. 533,863, filed on Sept. 20, 1983, entitled "A Process For Displaying A Plurality Of Objects On A Video Display Screen," and assigned to the present assignee. An improved VCS and video graphics controller are disclosed in U.S. Pat. Nos. 4,296,476 and 4,435,779 to Mayer, et al. (referred to below as the "Mayer '476 Patent" and "Mayer '779 Patent") entitled "Data Processing System With Programmable Graphics Generator," herein incorporated by reference. The VCS and video graphics controller disclosed in the Mayer '476 and '779 Patents employ many of the basic concepts taught in the earlier Mayer '422 Patent. For example, the Mayer '476 and '779 Patents teach the use of player and missile graphic registers to generate video graphics. Unlike the earlier Mayer '422 patent, however, the Mayer '476 and '779 Patents do disclose the use of both direct memory access (DMA) techniques and display lists to point to graphics data stored in memory.
While the later Mayer '476 and '779 Patents represented advances over prior art, the VCS and video graphics controller disclosed therein were not capable of compatibly executing graphics programs designed for the earlier model VCS which employed the TIA disclosed in the Mayer '422 Patent. In order to overcome this drawback, consumers were given the option of buying a peripheral adapter board which interfaced with the VCS disclosed in the Mayer '476 and '779 Patents, and which enabled the less sophisticated, but large, library of programs compatible with the earlier VCS to be executed thereon. The peripheral adapter board comprised a complete VCS with the TIA as disclosed in the Mayer '422 Patent. Since the graphics created by the VCS disclosed in the Mayer '476 and '779 Patents were considered to be only modestly more sophisticated than those created by the VCS and TIA disclosed in the earlier Mayer '422 patent, many consumers were not willing to pay the relatively large sums of money required to buty not the improved VCS, but also the interface adapter which would enable them to make use of an existing library of the video graphics programs designed for the predecessor model graphics controller.
The need existed to provide a video computer system which employs a video graphics controller which enables the display of greatly improved video graphics. In addition, the need exists to provide such a system which is selectively capable of executing video graphics programs from earlier systems without requiring the user to purchase expensive interface adapters.